Marc Nygaard struck twice - once from the penalty spot - as QPR staged a stunning second-half fightback to ease their relegation fears.
Leicester had completely dominated the opening 45 minutes but were frustrated by QPR goalkeeper Lee Camp, who kept his side on terms at the break with a series of fine saves.
The visitors desperately need to put together a winning sequence of results to pull clear of the drop zone but it was Leicester who made the brighter start and Camp was in action inside the opening two minutes to deny Iain Hume.
Leicester again threatened after nine minutes with Jason Jarrett letting fly from 20 yards but Camp was once again equal to it to keep his side level.
Just a minute later Leicester's Nils-Eric Johansson was booked for handball, although QPR continued to struggle to get out of their own half.
Jarrett had another chance after 15 minutes, following a fine cross from Johansson, only to steer his shot from 12 yards wide of the left-hand upright.
The visitors did finally carve out an opportunity shortly afterwards but Paul Furlong was unable to direct his header on target after getting on the end of a cross from Lee Cook.
But it was Leicester who continued to pepper the visiting goal from distance with Camp again tested by Alan Maybury's 25-yarder midway through the first half.
QPR's Damion Stewart followed Johannson into the referee's notebook following a foul on Hume as the home side continued to push for the opener.
The visitors' Danny Cullip was also booked just after the half-hour mark for a foul on Geoff Horsfield and from the resulting free-kick Camp again came to his side's rescue by parrying a 25-yard piledriver from Hume.
He was again in the thick of the action five minutes before the interval with an excellent save to keep out Stephen Hughes' shot from 18 yards.
Hume was booked on the stroke of half-time for a foul on QPR's Cook.
Having been under the cost for much of the first half though, it was QPR who took the lead just two minutes after the restart.
Nygaard found himself completely unmarked in the penalty area and his header teed up Inigo Idiakez who nodded home from close range to lift some of the pressure on his boss John Gregory.
And it got even better for Gregory just a couple of minutes later as his side doubled their advantage from the spot.
Furlong was fouled in the area by Shaun Newton and Nygaard drove home the penalty past Leicester goalkeeper Paul Henderson to put his side firmly in the driving seat.
Nygaard grabbed his second after 68 minutes with a superb 30-yard volley to wrap up the points before Leicester grabbed a last-gasp consolation when Hume scored from the penalty spot after Cullip had been penalised for handball.
Teams:
Leicester Henderson, Maybury, Kenton, Kisnorbo, Johansson,Newton, Jarrett (Wesolowski 76), Hughes (Tiatto 76), Yeates,Hume, Horsfield (Hammond 62).
Subs Not Used: Logan, Stearman.
Booked: Johansson, Hume.
Goals: Hume 90 pen.
QPR Camp, Mancienne, Cullip, Stewart, Bignot,Ainsworth (Smith 88), Bolder, Idiakez (Lomas 63), Cook,Furlong (Ray Jones 84), Nygaard.
Subs Not Used: Cole, Kanyuka.
Booked: Stewart, Cullip, Furlong, Ray Jones.
Goals: Idiakez 47, Nygaard 51 pen, 68.
Att: 24,558
Ref: N Swarbrick (Lancashire).